JP2015502052A - Edge-emitting etching facet laser - Google Patents

Abstract

A substrate and an epitaxial structure on the substrate, the epitaxial structure including an active region, the active region generating light, and an epitaxial structure extending in a first direction A waveguide having a front etched facet and a back etched facet defining an edge emitting laser and a first recessed region formed in the epitaxial structure at a distance from the waveguide A laser chip having an opening adjacent to the backside etched facet and having a first recessed area that facilitates testing of the adjacent laser chip prior to laser chip singulation. [Selection] Figure 1

Description

[Cross-reference of related applications]
This application includes US Provisional Application No. 61 / 568,383, filed Dec. 8, 2011, US Provisional Application No. 61 / 619,190, filed Apr. 2, 2012, and November 2011. The claims of priority to US non-provisional application No. 13 / 690,792 filed on May 30 are claimed, the entire contents of each of which are incorporated herein by reference.

  The present invention relates generally to etched faceted photonic devices, and more specifically to improved etched faceted photonic devices and methods for making them.

  A semiconductor laser typically grows an appropriate layered semiconductor material on a substrate through metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE) to produce an epitaxial structure having an active layer parallel to the substrate surface. By forming, it is fabricated on a wafer. The wafer is then processed by various semiconductor processing tools to produce a laser optical resonator that incorporates an active layer and a metal contact that is attached to the semiconductor material. Laser reflector facets are typically formed at the end of a laser resonator by cleaving a semiconductor material along its crystal structure to define the end face or end of the laser optical resonator, and as a result When a bias voltage is applied across the contact, the resulting current flow through the active layer causes the photons to exit the facet edge of the active layer and emit light in a direction perpendicular to the current flow. Become. Since the semiconductor material is cleaved to form laser facets, the location and orientation of the facets is limited, and once a wafer is cleaved, it typically becomes a small piece, resulting in conventional lithographic techniques. Can not be easily used to further process the laser.

  The foregoing and other difficulties arising from the use of cleaved facets have led to the development of processes for forming semiconductor laser reflector facets through etching. This process, described in US Pat. No. 4,851,368, also allows the laser to be monolithically integrated with other photonic devices on the same substrate. It also allows wafer level testing with reduced manufacturing costs instead of cleaved bar testing. This work has been further expanded, and an etching facet-based ridge laser process has been developed in accordance with IEEE Journal of Quantum Electronics, volume 28, no. 5, pages 1227-1231, May 1992. However, FP and DFB edge emitting lasers fabricated using etched facets are the most vulnerable to laser output interference from the front facet of the laser to the back facet of the adjacent laser that would distort the test results on the wafer. Close packing was not possible. The solution has been to separate the lasers and leave a useless space between adjacent lasers. For example, for a DFB laser, this wasted space is approximately 100 μm, which greatly reduces the number of useful laser chips that can be produced from a given wafer.

  In general, in one aspect, the invention features an edge emitting laser that can be fabricated while minimizing wasted space between adjacent lasers. The laser front etch facet is arranged on the back side of the adjacent laser chip so that light from the front facet of the first laser can be emitted without interference and back reflection from the back facet of the second adjacent laser. Facing the recessed area.

  The present invention may include a chip having an edge-emitting semiconductor laser with a first etching facet, the chip being adjacent to the chip containing the first laser by containing a recessed region, the front facet being a chip The edge-emitting semiconductor lasers of the second etching facet facing each other can be closely spaced from one another while avoiding distortion during testing of the characteristics of the second laser. This allows for a significant increase in the number of chips that can be produced from the wafer.

  Other embodiments include one or more of the following features. The recessed area can have a sloped end wall to minimize back reflections. The rear facet of the laser may also face a recessed area on the front side of an adjacent laser chip, which may have an angled end wall. The tips may have complete recessed areas or complete openings along their length and may be offset from each other to minimize back reflections.

  In one particular embodiment, the laser chip is a substrate and an epitaxial structure on the substrate, the epitaxial structure including an active region, the active region generating light, and a first A waveguide formed in a directionally extending epitaxial structure having a front etch facet and a back etch facet defining an edge emitting laser and a first recess formed in the epitaxial structure A concave region disposed at a distance from the waveguide and having an opening adjacent to the backside etched facet to facilitate testing of adjacent laser chips prior to laser chip singulation; 1 recessed area may be included.

  According to an additional aspect of this particular embodiment, the first recessed region has a first end wall.

  According to an additional aspect of this particular embodiment, the first end wall is at an angle other than perpendicular to the first direction.

  According to an additional aspect of this particular embodiment, the back etch facet is coated with a highly reflective material.

  According to an additional aspect of this particular embodiment, a laser chip is formed in the epitaxial structure having an opening adjacent to the front etch facet and disposed at a second distance from the waveguide. A second recessed area may further be included, the second recessed area including a second end wall.

  According to an additional aspect of this particular embodiment, the second end wall is at an angle other than perpendicular to the first direction.

  According to an additional aspect of this particular embodiment, the opening to the first recessed area and the opening to the second recessed area are aligned with each other.

  In another particular embodiment, the edge emitting laser is a ridge laser.

  According to an additional aspect of this particular embodiment, the ridge laser is of the Fabry-Perot (FP) type.

  According to an additional aspect of this particular embodiment, the ridge laser is of the distributed feedback (DFB) type.

  According to an additional aspect of this particular embodiment, the edge emitting laser is a buried heterostructure (BH) laser.

  According to an additional aspect of this particular embodiment, the BH laser is of the Fabry-Perot (FP) type.

  According to an additional aspect of this particular embodiment, the BH laser is of the distributed feedback (DFB) type.

  According to an additional aspect of this particular embodiment, the substrate is InP.

  According to an additional aspect of this particular embodiment, the substrate is GaAs.

  According to an additional aspect of this particular embodiment, the substrate is GaN.

  In another particular embodiment, a laser chip is a substrate and an epitaxial structure on the substrate, the epitaxial structure including an active region, the active region generating light, and a first A first waveguide formed in a directionally extending epitaxial structure, the first waveguide having a first front etch facet and a first back etch facet defining a first edge-emitting laser. A second waveguide formed in the waveguide and an epitaxial structure extending in a first direction, the second front etching facet and the second rear etching facet defining a second edge-emitting laser. A second waveguide and a recessed region formed in the epitaxial structure, the first backside etching facet and the second Has an opening adjacent to one of the rear surface etched facets, before singulation of the laser chip to facilitate testing of the adjacent laser chip may include a recessed area.

  According to an additional aspect of this particular embodiment, at least one of the first and second edge emitting lasers is a ridge distributed feedback (DFB) laser.

  According to an additional aspect of this particular embodiment, at least one of the first and second edge emitting lasers is a buried heterostructure (BH) distributed feedback (DFB) laser.

  In another particular embodiment, a laser chip is a substrate and an epitaxial structure on the substrate, the epitaxial structure including an active region, the active region generating light, and a first A waveguide formed in an epitaxial structure extending in a direction, having a front etching facet and a rear etching facet defining an edge emitting laser, and being in a direction parallel to and from the waveguide It may include a full opening in the epitaxial structure that facilitates testing of adjacent laser chips prior to singulation of the laser chip at a distance.

  The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the described embodiments will be apparent from the description and drawings, and from the claims.

  The foregoing and additional objects, features, and advantages will become apparent to those skilled in the art from the following detailed description of preferred embodiments thereof, taken in conjunction with the accompanying drawings.

It is a perspective view of an edge emitting etching facet laser. FIG. 2 is a top plan view of two adjacent edge emitting etch facet lasers similar to FIG. 1. Figure 5 shows the photocurrent versus spectral characteristics of an etched facet Fabry-Perot edge emitting etch facet laser with relatively small separation between adjacent lasers. Figure 5 shows the photocurrent versus spectral characteristics of an etched facet Fabry-Perot edge emitting etch facet laser with relatively small separation between adjacent lasers. Figure 2 shows the photo versus current and spectral characteristics of an etched faceted Fabry-Perot laser with relatively large separation between adjacent lasers. Figure 2 shows the photo versus current and spectral characteristics of an etched faceted Fabry-Perot laser with relatively large separation between adjacent lasers. 1 is a perspective view of an edge emitting etching facet laser according to the present invention. FIG. FIG. 6 is a top plan view of two adjacent edge emitting etch facet lasers according to the present invention similar to FIG. 1 is a top plan view of an adjacent edge emitting double resonator etched facet DFB laser according to the present invention. FIG. FIG. 4 is a top plan view of two adjacent edge emitting etched facet lasers where the laser chips are offset from each other in each row of lasers.

  FIG. 1 shows a perspective view of a substrate 90 having an epitaxially deposited waveguide structure including an active region 80 in which an etched facet laser including a ridge 40 is fabricated. Etch facet ridge laser mesas 10 and 20 are positioned on the substrate such that the front facet 50 of the laser corresponding to mesa 10 is at a distance 70 from the rear facet of the laser corresponding to mesa 20.

  FIG. 2 shows a top plan view of two adjacent etched facet ridge lasers similar to those in FIG. A wire bond pad 30 is provided to allow wire bonding to the pad and to allow current to be directed to the ridge to allow the laser to operate. Laser mesas 10 and 20 are positioned on chips 15 and 25, respectively. Chips 15 and 25 are formed through a singulation process along the lines defining the chip boundaries in FIG.

  The substrate 90 may be formed of, for example, a III-V type compound, or an alloy thereof, which may be suitably doped. A substrate such as InP is deposited on top of a continuous layer forming an optical waveguide including an active region 80, such as by epitaxial deposition such as metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). Includes top surface. The semiconductor laser structure includes upper and lower cladding regions formed from a lower index semiconductor material, such as InP, adjacent to the active region 80, which can be formed with InAIGaAs-based quantum wells and barriers. Also good. The lower cladding may be formed partially through epitaxial deposition and in part by using a substrate. For example, a 1310 nm light emitting epitaxial structure with the following layers on an InP substrate 90 can be used: 0.5 μm n-InP; 0.105 μm AlGaInAs subregion; containing five 6 nm thick compressive strained AlGaInAs quantum wells An active region 80; a 0.105 μm AlGaInAs senior region; a 1.65 μm thick p-InP upper cladding; and a heavily p-doped InGaAs cap layer, each sandwiched by a 10 nm tensile strained AlGaInAs barrier. The structure may also have a wet etch stop layer.

  One of the major benefits of etch facet lasers is that for cleaved facet lasers, testing is performed at the wafer level as opposed to bar level testing. However, the distance 70 must be large enough to prevent back reflection and interference from the back facet 60 to the front facet 50 in order to allow sufficient benefit of testing on the wafer. The front facet 50 is where most of the light emerges from the edge emitting laser corresponding to the mesa 10. For example, if the distance 70 is 50 μm for an InP-based 1310 nm Fabry-Perot (FP) ridge laser with a ridge width of about 2 μm, undesirable properties due to back reflection are observed in FIG. 3, where FIG. Indicates that the laser light-to-current (or LI) characteristics begin to change around 50 mA, and the corresponding problem appears in FIG. 3 (b) above 50 mA, ie, the spectral characteristics of the laser are 50 mA. And an abnormal double distribution of the FP mode. Each spectrum is offset for clarity in FIG. 3 (b).

  For a 13 μm FP laser with a 2 μm ridge width, increasing the distance 70 to 100 μm or more minimizes the effects from back reflection and interference, the adverse effects being the LI characteristics of FIG. ) In the spectrum (where each spectrum is offset for clarity). The spectral result in FIG. 4B shows a normal distribution of the FP mode. The distance 70 is also very important in testing on the wafer of a distributed feedback (DFB) laser where the grating is incorporated into the epitaxial structure. If the distance 70 is too small, back reflections can cause changes in the characteristics of the DFB laser, and as a result, the laser characteristics obtained after singulation may be different, greatly reducing the value of the test on the wafer. By selecting a distance 70 of 100 μm or more, the undesirable effect of back reflection is eliminated for the 1310 nm DFB laser. However, increasing the distance 70 to 100 μm or more is a useless space that significantly reduces the number of chips that can be obtained from the wafer.

  FIG. 5 shows a perspective view of a substrate 190 having an epitaxially deposited structure similar to that described above, including an active region 180, in which an etched facet laser including a ridge 140 is fabricated. The etching facet laser is such that the front and back facet planes of two adjacent laser mesas face each other (and correspondingly the back and front facet planes of the two adjacent laser mesas face each other). Above, it is arranged in an alternating fashion from front to back and back to front. In this arrangement, the etching ridge 140 of the laser mesa 110 is aligned with the recess 157 formed in the adjacent laser mesa 120. Etch facet ridge laser mesas 110 and 120 are positioned on the substrate such that the front facet 150 of the laser corresponding to mesa 110 is at a distance 170 from the wall 155 of the recessed area 157. The wall 155 can be at an angle other than normal to the incident laser beam to minimize back reflections to the front facet 150. The recessed area is about 5 μm deep so that the wall 155 is about 5 μm high and the floor of the recessed area is about 2.9 μm below the plane of the active area. In instances where the wall 155 is at an angle other than a right angle, the distance 170 can be reduced from 100 μm while avoiding a level of back reflection and interference that is detrimental to testing on the wafer.

  FIG. 6 illustrates a top plan view of two adjacent edge emitting etched facet lasers similar to FIG. In practice, the two adjacent edge emitting lasers of FIG. 6 are used as unit building blocks and are arranged on the wafer in rows and columns. The back facet 160 of the laser corresponding to the mesa 120 is coated with high reflectivity, so the effect of back reflection is not excessive. Nevertheless, a recessed area 167 is provided to minimize back reflection. The wall 165 of the recessed area 167 can also be at an angle other than normal to the incident laser beam to minimize back reflections to the back facet 160. Laser mesas 110 and 120 are positioned on chips 115 and 125, respectively. Chips 115 and 125 are formed through a singulation process along the lines defining the chip boundaries in FIG. Chip 115 including wire bond pad 130. The separation 175 between the laser mesas 110 and 120 is just large enough (around 10 μm) to allow singulation to occur. The minimization of separation 175 allowed a significantly larger number of laser chips to be produced from the same size wafer. Further, the recessed areas 157 or 167 may be formed at the same time as the dry etch facets and dry etch ridges are formed.

  FIG. 7 illustrates the application of the present invention to an example of two laser cavities per chip. Laser mesas 210 and 220 are positioned on chips 215 and 225, respectively. Chips 215 and 225 are formed through a singulation process along the lines defining the chip boundaries in FIG. Chip 215 includes two laser ridge resonators 240 and 241 with wire bond pads 230 and 231 respectively providing current to ridges 240 and 241. The ridge laser 240 has a front facet 250, and the ridge laser 241 has a front facet 251. Adjacent mesas have recessed areas 257 in front of facets 250 and 251. The recessed area has two wall 255 and 256 terminations that can be at an angle off normal to each laser beam emerging from facets 250 and 251 respectively. The distance 270 between the front facet 250 and the wall 255 is preferably greater than 100 μm, but could be shorter if the wall is at an angle to the right angle of the laser beam emerging from the facet 250. Similarly, the distance 271 between the front facet 251 and the wall 256 is preferably greater than 100 μm, but could be shorter if the wall is at an angle to the right angle of the laser beam emerging from the facet 251. . This allows laser mesas 210 and 220 to have minimal separation 275 to increase the number of chips that can be produced from a given wafer. The two laser back facets 260 and 261 in the mesa 220 may also face the recessed area 267 in the mesa 210 to minimize back reflections.

  Another alternative in accordance with the present invention is illustrated in FIG. 8, where etching facet edge emitting laser mesas 310, 320, 321, and 322 are positioned on chips 315, 325, 326, and 327, respectively, and the laser is , Having a ridge 340 and a wire bond pad 330 for providing current to the ridge, as illustrated for the laser corresponding to mesa 310. The recessed area 357 extends completely over the entire length of the chip on one side of the etching facet laser chip 320 to form a complete opening. In this way, the recessed area 357 extends to the rear facet 355 of the laser corresponding to the mesa 321. The rear facet 355 is normally perpendicular to the emitted laser light emerging from the front facet 350. Distance 370 is the distance between front facet 350 and rear facet 355. Laser mesas 310 and 320 have minimal separation 375 from top to bottom, similar to those in FIGS. 6 and 7, but laser mesas 321 and 322 also have minimal separation 376 from left to right. This further allows an increase in the number of chips that can be produced from a given wafer. The sides of the chip are only aligned from left to right, as opposed to the chips in FIGS. 6 and 7, which are aligned from left to right and from top to bottom. Singulation needs to respond to this fact, for example, singulation must first occur from left to right and then the chips are separated by top to bottom singulations. It will be appreciated that FIG. 8 and the above description are from the perspective of a single laser resonator per chip and that the same approach can be applied to more than one laser resonator per chip.

  The invention is described using a 1310 nm emitting laser based on an InP substrate. However, several other different epitaxial structures based on, for example, InP, GaAs, and GaN substrates can benefit from the present invention. For example, many embodiments of epitaxial structures that include active layers on these exemplary substrates that emit wavelengths in the infrared and visible spectral regions are available. Furthermore, although an edge emitting ridge laser with an etched ridge has been described, it will be appreciated that other types of etched facet lasers may be used, such as an etched faceted buried heterostructure (BH) laser.

  While the invention has been illustrated in terms of various embodiments, various changes and modifications can be made without departing from the true spirit and scope of the invention as set forth in the following claims. It will be understood that it is good. Further, it will be understood that the dimensions and ratios shown in the figures are not necessarily to scale, but are used to clearly illustrate the salient features of the structure and method.

Claims (20)

A laser chip,
A substrate,
An epitaxial structure on the substrate, the epitaxial structure including an active region, wherein the active region generates light; and
A waveguide formed in the epitaxial structure extending in a first direction, the waveguide having a front etch facet and a back etch facet defining an edge emitting laser;
A first recessed region formed in the epitaxial structure, disposed at a distance from the waveguide, and having an opening adjacent to the rear surface etching facet; A laser chip comprising a first recessed area that facilitates testing of adjacent laser chips prior to calibration.   The laser chip of claim 1, wherein the first recessed region has a first end wall.   The laser chip according to claim 2, wherein the first end wall is at an angle other than a right angle with respect to the first direction.   The laser chip of claim 3, wherein the back etch facet is coated with a highly reflective material.   A second recessed region formed in the epitaxial structure and disposed at a second distance from the waveguide and having an opening adjacent to the front etch facet; The laser chip of claim 1, wherein the recessed region includes a second end wall.   The laser chip according to claim 5, wherein the second end wall is at an angle other than a right angle with respect to the first direction.   The laser chip of claim 6, wherein the opening to the first recessed area and the opening to the second recessed area are aligned with each other.   The laser chip according to claim 1, wherein the edge emitting laser is a ridge laser.   The laser chip according to claim 8, wherein the ridge laser is of a Fabry-Perot (FP) type.   The laser chip according to claim 8, wherein the ridge laser is of a distributed feedback (DFB) type.   The laser chip according to claim 1, wherein the edge-emitting laser is a buried heterostructure (BH) laser.   The laser chip according to claim 11, wherein the BH laser is of a Fabry-Perot (FP) type.   The laser chip according to claim 11, wherein the BH laser is of a distributed feedback (DFB) type.   The laser chip according to claim 1, wherein the substrate is InP.   The laser chip according to claim 1, wherein the substrate is GaAs.   The laser chip according to claim 1, wherein the substrate is GaN. A laser chip,
A substrate,
An epitaxial structure on the substrate, the epitaxial structure including an active region, wherein the active region generates light; and
A first waveguide formed in the epitaxial structure extending in a first direction, having a first front etch facet and a first back etch facet defining a first edge-emitting laser; A first waveguide;
A second waveguide formed in the epitaxial structure extending in a first direction, having a second front etch facet and a second back etch facet defining a second edge-emitting laser; A second waveguide;
A recessed region formed in the epitaxial structure, and having an opening adjacent to one of the first rear surface etching facet and the second rear surface etching facet; Facilitates testing of adjacent laser chips prior to calibration. A laser chip comprising a recessed region.   The chip of claim 17, wherein at least one of the first and second edge emitting lasers is a ridge distributed feedback (DFB) laser.   The chip of claim 17, wherein at least one of the first and second edge emitting lasers is a buried heterostructure (BH) distributed feedback (DFB) laser. A laser chip,
A substrate,
An epitaxial structure on the substrate, the epitaxial structure including an active region, wherein the active region generates light; and
A waveguide formed in the epitaxial structure extending in a first direction, the waveguide having a front etch facet and a back etch facet defining an edge emitting laser;
A complete opening in the epitaxial structure in a direction parallel to the waveguide and at a distance from it to facilitate testing of adjacent laser chips prior to singulation of the laser chip A laser chip comprising a complete opening.

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